The present invention is directed to underground support systems for resisting and preventing the dangers associated with the collapse of geologic structures in underground excavations such as drifts or passages in mining operations.
In the past many types of supports have been proposed to stabilize and improve the support of geologic formations when disturbed by excavating drifts or passages to reach desirable materials, the recovery of which is economical and in most cases important. Mechanical supports have been relied upon in regard to the structure that follows the most successful methods of gaining stability of geologic formations.
In recent times, mine support systems employing cables instead of rods have been used. Cables have been anchored in cementeous materials over long lengths in metal mines to stabilize geologic structures. Rock anchors of this type are normally passive in nature, not loading the rock but allowing the rock load to move to the anchor, but on occasion they are post tensioned with cable bodies attached to the cable with wedges and roof plates. In U.S. Pat. No. 4,265,571, there is disclosed a cable truss support system which has been effective in resisting geologic movements. This system employed long drive anchors in the form of friction stabilizers to place the cable and anchors in cementeous material and to provide a tension in the cable truss upon installation. In U.S. Pat. No. 3,509,726 of May 5, 1970, there is disclosed a method of rod support across the mine opening employing mechanical anchors or resinous anchors and using threaded turnbuckles to adjust roof support. In U.S. Pat. No. 3,427,811 of Feb. 18, 1969, there is disclosed a support system employing flexible cables. In this disclosure, rod elements are disposed in the boreholes in the mine roof and the exposed ends are interconnected by a flexible cable arrangement utilizing a turnbuckle device to produce tension. In. U.S. Pat. No. 3,601,994 of Aug. 31, 1971, there is disclosed a roof support system for underground drifts having a flexible cable arrangement in which the opposite ends of the cables were anchored by wedge members exerting restrictive contact on the surface of the boreholes after the wedge members are driven home to apply desired tension on the cables. Others in this field have developed rod/truss systems using threaded rods extended across the roof which are refinements of the above described techniques.